My invention pertains to a non-linear filter circuit arrangement. More specifically, the invention pertains to a non-linear filter circuit arrangement for use in car space measurement systems in railroad classification yards to reduce the signal-to-noise ratio and thus overcome measurement errors due to poor shunting by cars moving along the various storage tracks.
In railroad classification yards, various electrical arrangements are used to measure the unoccupied space in each classification or storage track. This car space measurement, also called distance-to-go, is used as one factor in calculating the desired departure speed for controlling the various car retarders which establish the speed of the moving cars entering the classification tracks. Most of these measuring arrangements use a selected characteristic of rail current, which flows in a rail loop from the entry end of each storage track to the nearest car axle shunt, to determine the distance to the shunt, i.e., the remaining storage space. Fairly accurate measurements are obtained when cars are not in motion, but the data signal becomes very noisy when a car is moving along the track. This noise is caused by the poor shunting of a single car so that the shunt is sometimes through the rear truck of the car, sometimes through the front truck, and sometimes through neither. The noise depends strongly on the electrical conductivity of the rail surface and becomes very bad when the rail is quite rusty. Even under rusty rail conditions, there are occasional instances of good shunting. If a car has been acting as a poor shunt, then the occurrence of a good shunt will cause the car to appear to have moved backwards along the track. This apparent reverse movement is indicated since the signal being measured across the track at the entry end changes suddenly from a relatively high level to a low or minimum level, which then usually disappears and a high level reading is again received. Actually, the intermittent low readings are correct values of the instant distance measurement and the intervening and erratic larger readings are entirely meaningless. It is important, of course, to know that a car is still moving along the storage track toward the standing cars and to have some relatively accurate indication of its increasing distance down the track, so that the speed control of following cars directed to that track may be more efficiently controlled. Thus, some means to substantially reduce the effect of the noise level in the track measurements, in order to provide a more accurate distance measurement and thus more accurate speed control of the cars moving to coupling, is a desirable feature for classification yard control systems.
Accordingly, an object of my invention is a filter circuit arrangement having a non-linear response to input signal increases and decreases.
Another object of the invention is a non-linear filter circuit in which the output signal lags increases of the input signal level, but follows more closely as the input decreases.
A further object of my invention is a filter arrangement to improve the measurement of the distance to a moving shunt in a transmission channel when poor shunting conditions exist.
Another object of the invention is a non-linear filter arrangement for track distance measuring apparatus to reduce the effect of noise in rail current due to poor shunting by cars moving along the track.
A still further object of my invention is a non-linear filter to reduce noise due to erratic increases and decreases in an input voltage signal, the filter including a capacitor with a charging circuit having a relatively large time constant and a discharge circuit with a very much shorter time constant so as to reduce the output signal variations when the input increases, but to rapidly correct when the input decreases.
Still another object of the invention is a non-linear filter arrangement for reducing noise in distance measurement signals in a railroad yard due to intermittent and poor shunting of the track rails by cars moving along a storage track.
A yet further object of the invention is a filter arrangement for car space measuring apparatus in railroad yards to reduce the effect of poor shunting by moving cars by delaying increase in the distance signal storage when a rapid input level increase occurs due to loss of shunt and for rapidly varying the stored signal when the input decreases upon the renewal of the shunt to improve the accuracy of a continuously varying distance signal as a car travels along the track.
Other objects, features, and advantages of the invention will become apparent from the following specification and appended claims when taken in connection with the accompanying drawings.